and it all works well on server side, model is validated ok, and everything. But client side validation does not activate for this the second attribute, it works for Required, and it also works for StringLength but not for Email.
i have tried including both jquery and Microsoft ajax scripts, but there seems to be no difference.

In ScottGu's blog, he states that the custom validation if implemented like this should work without the need to add custom script.

thank You, this has worked. I assume that for any custom rules it would only be necessary to implement the IClientValidatable interface with adequate rule type for it to be added to collection of rules jQuery can perform client validation for.
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ZakMay 12 '11 at 6:01